Switch with function for assigning queue based on a declared transfer rate

ABSTRACT

In an asynchronous transfer mode switch, a plurality of queues is provided for accumulating transfer cells, and a queue assignment processing section, receives a message for establishing a connection and assigns to the connection one of the queues having a forwarding rate close to a declared rate included in the message and not exceeding the declared rate.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/123,138, filed May 19, 2008, which is a division of U.S. applicationSer. No. 10/795,299, filed Mar. 9, 2004, now U.S. Pat. No. 7,391,726issued Jun. 24, 2008, which is a division of U.S. application Ser. No.09/233,084, filed Jan. 19, 1999, now U.S. Pat. No. 6,731,603 issued May4, 2004, entitled: Asynchronous Transfer Mode Switch with Function forAssigning Queue Having Forwarding Rate Close to Declared Rate, and basedon Japanese Patent Application No. 10-020129, filed Jan. 19, 1998, byRyota MOTOBAYASHI, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an asynchronous transfer mode (ATM)switch for controlling traffic and, more particularly, it relates to anasynchronous transfer mode switch adapted to confine the transfer cellforwarding rate to a preselected forwarding rate.

2. Description of the Related Art

According to the ATM exchange technology, information from variousdifferent media including audio information and video information can betransmitted for telecommunications by using as units fixed length blocksthat are referred to as cells. Such cells typically have a 53-octetlength, of which a 5-octet length is used as a header section and theremaining 48-octet length is used as a user information section.Information to be used for identifying the destination of connection isincluded in the header section to realize a high speed switching bymeans of hardware. Additionally, since information can be transferredwhenever it needs to be forwarded with the ATM, the existing rate can beutilized effectively and efficiently.

In a prior art ATM switch, an unspecified bit rate (UBR) type switchedvirtual connection (SVC) is used, so that a plurality of connections canbe assigned to one queue of a shaping processing section, if theconnections have the same declared rate. This will be explained later indetail.

Note that JP-A-8-125668 titled “ATM interface and Shaping Method”describes a technique, with which a “shaping” operation is performed bystoring in advance the largest cell forwarding interval corresponding toeach traffic condition that gives rise to an ATM cell portion discardedby the usage parameter control (UPC) for the virtual path identifier(VPI) and also for the virtual channel identifier (VCI) and, uponarrival of the ATM cell to be forwarded, forwarding it to an idleforwarding time slot according to the stored largest cell forwardinginterval.

Also, JP-A-8-288951 titled “ATM Switch and Congestion Control Method forATM-LAN” described a technique of selecting a backward explicitcongestion notification (BECN) system for dealing with congestion bynarrowing the transmission rate all the regions including the ATM localnetworks (LANs) containing respectively a transmission terminal and areception terminal and also covering the transmission terminal and thereception terminal upon receiving a notification from a congested ATMswitch depending on the site of congestion, a fast reservation protocol(FRP) system for dealing with congestion by forwarding a signal celladapted to broaden the transmission rate for the downstream uponreceiving a notification from the congested ATM switch and a forwardexplicit congestion notification (FECN) system for writing theidentifier for “the occurrence of congestion” in the payload type (PT)of the cell header forwarded from the congested ATM switch and causingthe reception terminal receiving the identifier to notify thetransmission terminal so as to broaden the transmission rate, whicheveris optimum, depending on the conditions of connection.

The prior art ATM switch, however, does not have a simplifiedconfiguration and is not adapted to assign optimum queues by using theUBR type SVC system. That is, if there are requests for connectionrequiring queues exceeding the number of queues constituting a cellbuffer it has for shaping, it is impossible to effectively control thecommunication traffic.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ATM switch havinga simplified configuration and adapted to assign optimum queues,particularly by using the UBR type SVC system.

According to the present invention, in an asynchronous transfer modeswitch a plurality of queues are provided for accumulating transfercells, and a queue assignment processing section receives a message forestablishing a connection and assigns to the connection one of thequeues having a forwarding rate close to a declared rate included in themessage and not exceeding the declared rate.

Thus, even if connections do not have the same declared rate, one queuecan be assigned to the connections without remarkably deteriorating thecommunication quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below, as compared with the prior art, withreference to the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a prior art ATM network;

FIG. 2 is a block circuit diagram illustrating one of the ATM switchesof FIG. 1;

FIG. 3 is a diagram for explaining the operation of the UPC section ofFIG. 2;

FIG. 4 is a diagram for explaining the operation of the shaping sectionof FIG. 2;

FIG. 5 is a block circuit diagram illustrating an embodiment of the ATMswitch according to the present invention;

FIG. 6 is a detailed block circuit diagram of the shaping processingsection of FIG. 5;

FIG. 7 is a flowchart showing the operation of the connection assignmentprocessing section of FIG. 5;

FIG. 8 is a diagram for explaining the assignment of an optimum CBRqueue in the shaping processing section of FIG. 6; and

FIG. 9 is a diagram for explaining the assignment of an optimum UBRqueue in the shaping processing section of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before the description of the preferred embodiment, a prior art shapingmethod will be explained with reference to FIGS. 1, 2, 3 and 4.

In FIG. 1, which illustrates a prior art ATM network utilizing the ATMtechnology, this ATM network is adapted to transmit sophisticatedinformation including moving pictures for the user and provide the userwith services in a way more responsive to the user's needs than comparedwith conventional networks. This ATM network is constructed by aplurality of ATM local area networks (LANs), such as 11 ₁ and 11 ₂ whichare private networks including private branch exchanges, and an ATM widearea network (WAN) 10 for connecting the ATM-LANs 11 ₁ and 11 ₂, theATM-WAN 10 being a public network.

The ATM-WAN 10 has a plurality of ATM switches 12 ₁, . . . , 12 _(N) init. The ATM switch 12 ₁ is connected to an ATM switch 13 ₁ in theATM-LAN 11 ₁ by way of a communication line 14 ₁. The ATM switch 12 _(N)is connected to an ATM switch 13 ₂ in the ATM-LAN 11 ₂ by way of acommunication line 14 ₂. The lines from the ATM-LAM 11 ₁, ATM-WAN 11 ₂and so on are mutually connected in the ATM-WAN 10 to form acommunication connection. Each of the ATM-LAN 11 ₁ and the ATM-LAN 11 ₂has a plurality of users (not shown) connected to it, and the users cancommunicate with one another within the LAN. Such a LAN is normally usedas a network covering a limited area, which may typically be a school ora commercial company, and controlled within the network area to which itbelongs.

The administrator of the ATM-WAN 10 concludes contracts with subscriberswho operate the ATM-LAN 11 ₁ and the ATM-LAN 11 ₂ for the networkservices it provides with rate to be used for the services in the formof “bits per second” or “cells per second” in advance. The rates thatare made available for the subscribers under the contracts are used asthe basis for calculating the telecommunications charges for the networkservices provided by the ATM-WAN 10 and also for determining the amountof capital investment that may be required for the additional rates ofcommunication lines to be provided within the ATM-WAN 10. Note that theexpression “bits per second” referring to the number of bits to betransmitted per second and the expression “cells per second” referringto the number of cells to be transmitted per second are synonymouslyused. For example, for ATM telecommunications conforming to therecommendation 1.361 of International TelecommunicationUnion-Telecommunication Standardization Sector (ITU-T), a cell isdefined to have a 53-octet length and hence “cells per second’=‘bits persecond’(53×8).”

Then, under such contracts, any of the users of the ATM-LAN 11 ₁ and theATM-LAN 11 ₂ can access any of the resources of the networks by way ofthe ATM-WAN 10. Since each of the ATM-LAN 11 ₁ and the ATM-LAN 11 ₂ hasa configuration optimally adapted to the environment of the network andis not profit-oriented, each of the users normally does not have to payattention to the cost of telecommunications within the network to whichhe or she belongs. On the other hand, the ATM-WAN 10 is a public networkand communication data can flow into it from other LANs (not shown). Forexample, if one of the users of the ATM-LAN 11 ₁ caused trafficexceeding the operating rate for which the user had contracted to flowinto the ATM-WAY 10, he or she may use one or more additionalcommunication rates allocated to the remaining users. Then, theadministrator of the ATM-WAN 10 may become unable to provide thesubscribers with services to which the subscribers are entitled underthe contracts. Therefore, the ATM switches that are used in LANs andWANs are normally so arranged as to control the communication traffic insuch a way that the users may be provided with optimal services and sucha situation may appropriately be avoided.

FIG. 2 is a block circuit diagram of one of the ATM switches of FIG. 1for controlling a communication traffic, showing only principalcomponents thereof. In order to facilitate the understanding of theprinciple of the operation of controlling a communication traffic, it isassumed here that an ATM switch 20 is connected between a transmissionterminal 21 ₁ and a reception terminal 21 ₂, so that ATM transfer cellsare transferred from the transmission terminal 21 ₁ to the receptionterminal 21 ₂. Thus, the ATM switch 20 exchange communication data withthe transmission terminal 21 ₁ and the reception terminal 21 ₂ by way oflines 22 ₁ and 22 ₂, respectively.

The ATM switch 20 is constructed by a switch 201 for connecting an inputline and an output line assigned to a preselected connection, a usageparameter control (UPC) section 202 arranged upstream toward the inputside relative to the switch 201 for identifying the virtual pathidentifier (VPI) and the virtual channel identifier (VCI) of an ATMtransfer cell flowing in from the transmission terminal 21 ₁ by way ofthe line 22 ₁ and monitoring if the cell is transferred with apredetermined rate, and a shaping section 203 arranged downstream towardthe output side relative to the switch 201 for controlling theforwarding rate of the transfer cell by controlling the priority of thetransfer cells and buffering the transfer cells so that the rate of theline 22 ₂ for the output to the reception terminal 21 ₂ may not beexceeded. The UPC section 202 and the shaping section 203 are controlledby a connection admission control (CAC) section 204 in accordance withthe destination of the connection that is notified when the selectedconnection is established prior to the cell transfer, the declared valuefor the cell forwarding rate, and the priority.

The UPC section 212 monitors the traffic from the transmission terminal21 ₁ in accordance with the rate declared when the selected connectionis established so that it may not flow in excessively. In other words,so long as the traffic from the communication terminal 21 ₁ does notexceed the declared rate, it is transferred to the switch 201 withoutobstruction. However, once the traffic exceeds the declared rate, theexcessive cells are processed by means of an optimal method selectedfrom the following processing methods as a function of the specificfield of ATM telecommunications of the traffic. The processing methodsinclude (1) a method of simply discarding the excessive portion of thetraffic, (2) a method of marking the excessive portion of the trafficand selectively discarding the marked excessive portion when the networkis congested or billing an extra communication charge for that portion,and (3) a method of delaying the excessive portion of the traffic untilan idle time slot of the network is found. However, the marking method(2) or the delaying method (3) requires the use of an additional circuitand involves a complex processing operation which consequently raisesthe cost of telecommunication. Particularly, the delaying method (3) isaccompanied by the problem of delay time and hence is applicable only toa limited field of ATM telecommunications. On the other hand, thediscarding method (1) can simplify the configuration of the networkmost.

The shaping section 203 controls the forwarding rate by accumulating thecells to be forwarded in the buffering assigned to each connection, sothat the predetermined forwarding rate may not be exceeded and asituation where the portion exceeding the declared rate is discarded bythe UPC section 202 at the next stage ATM switch may be avoided.

When the ATM switch as illustrated in FIG. 2 is applied to the ATMnetwork as illustrated in FIG. 1, an ATM switch that functionssubstantially the same as the shaping section 203 is used for both theATM switch 13 ₁ of the ATM-LAN 11 ₁ and the ATM switch 13 ₂ of theATM-LAN 11 ₂ while an ATM switch that functions substantially the sameas the UPC section 202 is used for both the ATM switch 12 ₁ and the ATMswitch 12 ₂ of the ATM-WAN 10. Since the ATM-WAN 10 has a functioncorresponding to that of the UPC section 202 in it, a situation wherethe portion exceeding the declared rate is discarded in the ATM-WAN 10can be effectively avoided by shaping and limiting the rate forwardedfrom the ATM-LANs 11 ₁ and 11 ₂.

FIG. 3 is a diagram for explaining the operation of the UPC section 202of FIG. 2 for controlling the traffic from the ATM-LAN 11 ₁ to theATM-LAN 11 ₂ in accordance with the declared rate. It will be seen thattraffic Bu that changes with time relative to the contract value Bcpredetermined by the administrator of the ATM-LAN 11 ₁ is made to flowinto the ATM-WAN 10. If the rate Bu exceeds the contract rate Bc and ismade to flow into the ATM-WAN 10 on purpose, by mistake or for someother reason, the administrator of the ATM-WAN 10 may discard theexcessive portion Bd (=Bu−Bc) of the traffic exceeding the contractvalue Bc according to any of the above described methods. The operationof monitoring whether every subscriber of the ATM-LAN 11 ₁ is properlyobserving the contract rate Bc or not by means of the UPC section 202 ofthe ATM switch 12 ₁ of the ATM-WAN 10 is referred to simply as “UPC” or“policing.” With this operation, the traffic can be controlled withinthe ATM-WAN 10 in accordance with the contract rate, so that othersubscribers may not be adversely affected.

FIG. 4 is a diagram for explaining the operation the shaping section 203for controlling the traffic from the ATM-LAN 11 ₁ to the ATM-WAN 10. Theadministrator of the ATM-LAN 11 ₁ limits the rate Bu being forwardedthat changes with time by means of the shaping section 203 so that itmay remain within the contract rate Bc. The forwarding control operationof the shaping section 203 is referred to as “traffic shaping” or simplyas “shaping.” With this arrangement, the rate forwarded from the ATM-LAN11 ₁ can reliably be limited by the “shaping” so as not to exceed therate under the control of the “UPC” of the ATM-WAN 10, and hence thetraffic rate flowing into the ATM-WAN 10 may not exceed the contractrate Bc. Thus, no portion of the traffic forwarded from the ATM-LAN 11 ₁will be discarded for the reason of violating the contract if it exceedsthe contract value Bc.

The shaping section 203 is constructed by a cell buffer formed by afirst-in first-out memory and adapted to temporarily accumulate thecells flowing toward the ATM-WAN 10 from the ATM-LAN 11 ₁ and forwardthem to the ATM-WAN 10 with a rate not exceeding the contract rate Bc.

In each of the ATM-LANs 11 ₁ and 11 ₂, the connection from the relatedterminal is then connected to the ATM-WAN 10 by way of ATM switchesarranged in a plurality of stages. Thus, the cell transfer intervals can“fluctuate” or change irregularly to show “sparseness” and “denseness,”which by turn can give rise to fluctuations in the cell transfer delaywithin the ATM-LAN or the cell transfer delay due to some other reasonson the part of the traffic. If, for example, the transfer intervals ofthe cells belonging to the same connection become “dense” in thetelecommunication traffic, the forwarded rate of the connection canexceed the contract rate Bc before it flows into the ATM-WAN 10.Therefore, the cell buffer is used to absorb the “fluctuations” so thatthe forwarded rate may constantly remain below the contract rate Bc.

The cell buffer (shaper) is generally constructed by establishing aplurality of juxtaposed queues in a memory device and a rate is selectedfor each of the queues to determine the rate of reading data therefrom.A connection requesting to be connected can be “shaped” by selecting oneof the queues of a rate that seems optimal for the connection out of thequeues and assigning it to the connection.

In a permanent virtual connection (PVC) system, each of theadministrator of the ATM-LANs 11 ₁ and 11 ₂ and the ATM-WAN 10 selects arate for each queue in advance to establish the connection by taking theusers of each of the networks and the state of utilization of thenetwork into consideration and the connection itself is selected at thesame time. With this system, a queue that seems to be optimal can beselected as a very close queue with a rate not exceeding the contractrate Bc is selected for the connection selected by the administrator.However, the PVC system is accompanied by a problem of increasing thenumber of rates and carrying out a cumbersome reselecting operation thatoccurs each time a new user enters the scene.

On the other hand, in view of the circumstances where informationtransfer operations are required to be carried out with every possiblerate to adapt themselves to an ever increasing diversity of informationto be transferred, there is a strong demand for a connection methodusing a switched virtual connection (SVC) system for establishing aconnection with any given partner at any time at any selected rate sothat services may be provided in a more flexible fashion.

Also, the SVC system is divided into a constant bit rate (CBR) systemand an unspecified bit rate (UBR) system.

In the CBR system, a connection occupies the queues constituting a cellbuffer to determine the partner each time a communication is started, sothat another connection cannot be assigned in a multiplexed fashion.

In the UBR system, if two or more connections have the identical rate,the two or more connections are assigned to one of the queues.

In the UBR system, however, if the rate of one connection is a littledeviated from the rate of another connection, it is possible to assignthe same queue to them. Thus, since the number of queues constituting acell buffer is inevitably limited (e.g. to eight queues) depending onthe conditions of the ATM switch including the surface area for mountingthe electronic circuit components and other hardware components if therearises a connection requiring queues exceeding this number, there is noway to assign queues to the connection so that the conventionalcongestion control can remain baseless. For example, an ordinary ATMswitch cannot deal with thousands of connections simultaneously;however, the number of connections is actually limited to eight, forexample, in view of the number of queues.

Additionally, while the rate of the connection to be established isselected according to the peak rate or a rate close to that peak rate,the cell intervals getting to the queue are rather irregular andvariable depending on the conditions of the network and hence do notalways show the peak rate. As a result, the resources including thequeues may not necessarily be effectively and efficiently utilized tofully exploit the forwarding potential of the rates of the network.

In FIG. 5, which illustrates an embodiment of the ATM switch accordingto the present invention, only the principal elements thereof relatingto a “shaping” operation are illustrated. An ATM switch 50 isconstructed by a plurality of input line 51 ₁, 51 ₂, 51 ₃, 51 ₄, . . . ,51 _(N), a switch section 52, and a plurality of output lines 53 ₁, 53₂, 53 ₃, 53 ₄, . . . 53 _(N). The switch section 52 connects the inputlines 51 ₁, 51 ₂, 51 ₃, 51 ₄, . . . 51 _(N) to the output lines 53 ₁, 53₂, 53 ₃, 53 ₄, . . . 53 _(N) in accordance with the VPI and the VCIwritten in the header section of an ATM cell. Shaping processingsections 54 ₁, 54 ₂, 54 ₃, 54 ₄, . . . , 54 _(N) are provided in theoutput lines 53 ₁, 53 ₂, 53 ₃, 53 ₄, . . . 53 _(N), each having aplurality of queues. A transfer data is forwarded from the ATM switch 50by way of one of the shaping processing sections 54 ₁, 54 ₂, 54 ₃, 54 ₄,. . . 54 _(N).

Also, a connection assignment processing section 55, when a connectionestablishing request is received with a call from the transmissionterminal of an ATM-LAN (not shown), it assigns one or more queues of thecorresponding one of the shaping processing sections 54 ₁ through 54_(N) by referring to the declared rate contained in a call selectionmessage for establishing the connection.

Further, the ATM switch 50 includes a shaping setting section 56 forsetting a forwarding rate for each of the shaping processing sections 54₁ through 54 _(N) by way of a service provider interface 57 of a serviceprovider interface system (not shown) and defining the attribute of eachcell to be accumulated.

Now, the configuration of the shaping processing sections 54 ₁ through54 _(N) will be explained to illustrate the forwarding rate and the cellattribute set by the shaping setting section 56.

In FIG. 6, which illustrates the shaping processing section such as 54 ₂of FIG. 5, the shaping processing section 54 ₂ is constructed by a queuesection 60 for a PVC system, a queue section 61 for a CBR system of anSVC system, and a queue section 62 for a UBR system of the SVC system.

The attributes such as PVC, CBR and UBR of each connection are set bythe shaping setting section 56.

The queue section 60 is constructed by a PVC queue 60 ₁ having aforwarding rate B₀₁, and a PVC queue 60 ₂ having a forwarding rate B₀₂,. . . . Here,B₀₁<B₀₂< . . . .

The queue section 61 is constructed by a CBR queue 61 ₁ having aforwarding rate B₁₁, and a CBR queue 61 ₂ having a forwarding rate B₁₂,. . . . Here,B₁₁<B₁₂< . . . .

The queue section 62 is constructed by a UBR queue 62, having aforwarding rate B₂₁, and a UBR queue 62 ₂ having a forwarding rate B₂₂,. . . . Here,B₂₁<B₂₂< . . . .

As described above, a PVC system and the SVC system may be used for anATM telecommunication system. Since the administrator carries out aconnection with the PVC system, he or she can also set one of the queuesto be used for the connection so that an optimum queue may be assignedto the connection with the related rate. On the other hand, with the SVCsystem, since the rate of the line to be used for a connection issecured in accordance with the declared rate provided with a call from aterminal, it is difficult for the administrator to recognize the type oftraffic in advance and set an optimum queue unlike the case of the PVCsystem. Thus, different attributes may be used for the CBR and UBRsystem as described above to effectively utilize the rates.

In the case of the CBR system, traffic always occurs with a peak cellrate (PCR). Thus, if there is a CBR connection with a PCR of 10megabits/sec, there always occurs traffic with a PCR of 10 megabits/sec.Assume then a queue having a forwarding rate of 10 megabits/sec isassigned to the CBR connection. If the queue is assigned to another CBRconnection with a PCR of 10 megabits/sec, cells will have to bediscarded as excessive traffic with an average of 5 megabits/sec foreach of the two connections. Thus, it is highly desirable that a queueto be exclusively used for the CBR system is assigned to a CBRconnection in order to avoid a situation where the same queue isduplicately assigned to two connections.

On the other hand, in the case of the UBR system, the same queue may beassigned to a plurality of connections in a multiplexed fashion becausetraffic does not necessarily occur at PCR unlike the case of the CBRsystem. Thus, the same queue having a forwarding rate of 10megabits/sec, for example, may be assigned to a plurality of connectionsof UBR calls with a PCR of 10 megabits/sec in a multiplexed manner.

As described above, queues are used discriminately for the CBR systemthat does not allow any multiplexed assignment and for the UBR systemthat allows multiplexed assignment to take the characteristic featuresof the CBR and UBR systems into consideration, so that an optimum queuemay be assigned without difficulty to any connection that occurs with acall of the SVC system. Since the administrator recognizes the type ofconnection to be established in the case of the PVC system, he or shecan determine whether or not a single queue can be assigned to aplurality of connections and, therefore, it is not necessary todiscriminate the CBR and UBR systems.

The operation of the connection assignment processing section 55 will beexplained next with reference to FIG. 7. The connection assignmentprocessing section 55 is designed to assign an optimum queue having apredetermined rate and adapted to the attribute of a connection out ofthe shaping processing sections 54 ₁ through 54 _(N) in accordance withthe declared rate contained in a call selection message for establishingthe connection. Note that the connection assignment processing section55 is constructed by a central processing unit (CPU), a read only memory(ROM), and a random access memory (RAM), so that the CPU may assign anoptimum queue to the connection in accordance with the connectionassignment procedure stored in the ROM.

First, at step 701, it is determined whether or not a connectionestablishing request from a transmission terminal is a call selectionmessage. Only when such a connection establishing request is received,does the control proceed to step 702. Otherwise, the control returns tostep 701 which continues to wait for the reception of a connectionestablishing request.

At step 702, it is determined whether the connection to be establishedis of the SVC system, or of the PVC system on the basis of the receivedcall selection message. If it is determined that the connection is ofthe SVC system, the control proceeds to step 703. On the other hand, ifit is determined that the connection is of the PVC system, the controlproceeds to step 713.

At step 703, the attribute of the connection to be established isextracted from the call selection message. The attribute of theconnection represents whether the connection is of the CBR system or theUBR system on the basis of the call selection message. Then, at step704, the declared rate contained in the same call selection message isextracted.

Next, at step 705, it is determined whether the connection of the callis a CBR call. As a result, if the attribute of the connection is a CBRcall, the control proceeds to step 706 which selects an output line forthe connection in accordance with the VPI and the VCI of the connectionand, at the same time, specifies an optimum CBR queue such as 61 ₁, 61₂, . . . out of the queue section 61 assigned in advance by theadministrator from the shaping processing section corresponding to theoutput line.

For specifying the optimum CBR queue at step 706, the assigned queuewith the very close rate not exceeding the declared rate extracted atstep 704 is selected. If the forwarding rate B₁₂≦declared rate<theforwarding rate B₁₃, the CBR queue 61 ₂ is specified as the optimum CBRqueue that can be specified with ease by making the queues with the sameconnection attribute CBR having different forwarding rates. For extremesimplification, it may be so arranged that a call is not received whenthere is no CBR queue to be forwarded with a very close forwarding ratenot exceeding the declared rate.

Next, at step 707, it is determined whether or not the specified CBRqueue is occupied. As a result, when the specified CBR queue isoccupied, the control proceeds to step 708 which does not receive thecall but releases the call. On the other hand, when the specified CBRqueue is not occupied, the control proceeds to step 709 which assignsthe specified CBR queue to the connection to be established as requestedby the call.

On the other hand, at step 705, if the attribute of the connection isnot a CBR call, the control proceeds to step 710 which determineswhether or not the connection is a UBR call. As a result, only when theconnection is a UBR call, does the control proceed to step 711 whichselects an output line for the connection in accordance with the VPI andthe VCI of the connection and, at the same time, specifies an optimumUBR queue out of the queue section 62 assigned in advance by theadministrator from the shaping processing section corresponding to theoutput line in a manner as described above for specifying an optimum CBRqueue at step 705.

For specifying the optimum queue UBR at step 711, the assigned queuewith the very close rate not exceeding the declared rate extracted atstep 704 is selected. If the forwarding rate B₂₂≦declared rate<theforwarding rate B₂₃, the UBR queue 62 ₂ is specified as the optimum UBRqueue for the connection.

Next, at step 712, the specified UBR queue is assigned to theconnection. Since the attribute refers to a UBR call, the same UBR queuecan be assigned to a plurality of connections.

On the other hand, at step 702, if it is determined that the connectionto be established is not of the SVC system on the basis of the callselection message, the control proceeds to step 713 which sets the PVCsystem for the call.

Assuming that the rates as illustrated in FIG. 6 are selected for thequeues of the shaping processing sections 54 ₁ through 54 _(n) insertedbetween the switch section 52 and administrator as described above, theoperation to be carried out when a CBR call having a relationship of theforwarding rate B₁₂≦“declared rate of the connection”<the forwardingrate B₁₃ is made will be explained next with reference to FIG. 8.

Upon receiving a CBR call, the CPU of the connection assignmentprocessing section 55 determines whether or not the call requesting forconnection is of the SVC system in accordance with the call selectionmessage of the CBR call. The CPU additionally extracts the declared ratecontained in the call selection message of the SVC system because thecall is a CBR call. Then, the CPU further determines whether the call isa CBR call or a UBR call. After determining that the call is a CBR calland seeing that the declared rate is defined by the formula of theforwarding rate B₁₃≦“declared rate of the connection”<the forwardingrate B₁₃, the CBR queue 61 ₂ having the forwarding rate value B₁₂ isselected out of the CBR queue section 61 having a very close rate notexceeding the declared rate. Since no queue is allowed to be duplicatelyassigned for a CBR call as described above, the CPU determines whetheror not the queue has been assigned to some other connection and, if itis found that the queue has not been assigned to any other connection,it assigns the selected CBR queue as indicated by 81 in FIG. 8. If, onthe other hand, it is found that the CBR queue is occupied, the call isnot received and subjected to a predetermined call releasing processbefore it is released.

Now, assuming that the rates as illustrated in FIG. 6 are selected forthe queues of the shaping processing sections 54 ₁ through 54 _(N)inserted between the switch section 52 and the respective output lines53 ₁ through 53 _(n) by the administrator as described above, theoperation to be carried out when a UBR call having a relationship of theforwarding rate B₂₂≦“declared rate of the connection”<the forwardingrate B₂₃ is made will be explained next with reference to FIG. 9.

Assume here that the traffic from the input line 51 ₁ is of the UBRsystem and the UBR queue 62 ₂ of the shaping processing section 54 ₂corresponding to the output line 53 ₂ is assigned to it as indicated by91 in FIG. 9, when a new connection establishing request is made to theoutput line 53 ₂ from the input line 51 _(N).

Firstly, upon receiving a UBR call, the CPU of the connection assignmentprocessing section 55 determines whether or not the call requestingconnection is of the SVC system in accordance with the call selectionmessage of the UBR call. The CPU additionally extracts the declared ratecontained in the call selection message of the UBR call. The CPUadditionally extracts the declared rate contained in the call selectionmessage of the SVC system because the call is a UBR call. Then, the CPUfurther determines whether the call is a CBR call or a UBR call. Afterdetermining that the call is a UBR call and seeing that the declaredrate is defined by the formula of the forwarding rate B₂₂≦“declared rateof the connection”<the forwarding rate B₂₃, the UBR queue 62 ₂ havingthe forwarding rate B₂₂ is selected out of the queue section 61 having avery close rate not exceeding the declared rate. Since a UBR queue canbe duplicatively assigned for an UBR call as described above, the CPUcan assign the selected queue without any further operation as indicatedby 92 in FIG. 9.

In the case of an ATM switch having a “shaping” function as describedabove, the relationship of ‘the rate forwarded from the ATM-LAN’≦‘therate of the UPC of the ATM-WAN’” always holds true so long as thedownstream ATM switch having a “UPC” function can recognize the declaredrate so that the “UPC” function of the ATM-WAN eliminates cellsexceeding the rate to avoid a situation where cells are discarded fornothing.

In the above-described embodiment, while the connection assignmentprocessing section 55 does not accept a CBR call and simply releases itin the operation of assigning a CBR queue to the CBR call if the CBRqueue has been assigned to some other connection, another CBR queue mayalternatively be selected if this CBR queue has a narrower rate. Forexample, in the case of FIG. 9, the CBR queue 61 ₁ having the forwardingrate value B₁₁ may be selected.

Additionally, while the above described embodiment is adapted to selecta queue with a very close forwarding rate not exceeding the declaredrate, the essential requirement to be met for the present invention isthe selection of a queue with a rate not exceeding the declared rate,which is not necessarily a very close rate, although the selection of aqueue with a rate that falls too short of the declared rate canremarkably degrade the quality of telecommunications of thetelecommunication rate requested by the transmission terminal.

Still additionally, while the arrangement of assigning a single queue toa plurality of connections of this embodiment is subjected to arestriction that the total sum of the rates of these connections shouldnot exceed the rate selected for the queue, it can operate veryeffectively particularly when the number of connection requests (e.g.,several thousands) exceeds by far the limited number of available queues(e.g., several queues) and to avoid “UPC” that can be caused by thedownstream ATM switch is the top priority.

Still additionally, although the ATM switch is used as a gate wayconnecting ATM-LANs and an ATM-WAN, it may alternatively be used as ageneral purpose telecommunication traffic control apparatus arrangedupstream relative to an ATM switch having the “UPC” function andoperated by means of the “shaping” function of the upstream ATM switchand the “UPC” function of the downstream ATM switch.

Finally, while the attribute of the traffic is described in terms of CBRand UBR for the embodiment, shaping assignment can be used for someother traffic defined in terms of variable bit rate (VBR) or availablebit rate (ABR) typically by referring to the traffic parameters otherthan the PCR contained in the call selection message.

As explained hereinabove, according to the present invention, anasynchronous transfer mode switch can be simplified and adapted toassign optimum queues by using the SVC system, particularly, the UBRsystem thereof, and also to control the communication traffic inresponse to the request of a connection requiring queues exceeding thenumber of queues constituting a cell buffer it has for shaping.

1. A network device comprising: a set of queues to buffer dataassociated with a plurality of connection requests, received at thenetwork device, from a plurality of terminals; and a processor to:identify a declared transfer rate associated with a particularconnection request, of the plurality of connection requests, containingparticular traffic parameters other than a peak cell rate (PCR),determine, based on the particular traffic parameters, particularqueues, of the set of queues, having forwarding rates that are notgreater than the declared transfer rate, and assign an unoccupied queue,of the particular queues, to the particular connection request.
 2. Thenetwork device of claim 1, where the particular traffic parameterscomprise at least one of a variable bit rate (VBR) or an available bitrate (ABR).
 3. The network device of claim 1, where the processor isfurther to: determine that the particular connection request is aswitched connection, and identify an attribute associated with theparticular connection request.
 4. The network device of claim 1, wherethe processor is further to: identify another declared transfer rateassociated with another connection request, of the plurality ofconnection requests, containing the PCR associated with the otherconnection request, determine, based on the PCR, other particularqueues, of the set of queues, having forwarding rates that are notgreater than the other declared transfer rate, and assign an occupiedqueue, of the other particular queues, to the other connection request.5. The network device of claim 1, where the processor is further to:select a particular output line, of a plurality of output lines of thenetwork device, corresponding to the unoccupied queue, where theprocessor assigns the unoccupied queue and selects the particular outputline substantially concurrently.
 6. The network device of claim 1,where, when the processor assigns the unoccupied queue, the processor isfurther to: determine that the forwarding rate of the unoccupied queueis greater than the forwarding rate of each of the other queues, of theparticular queues, and select the unoccupied queue based on thedetermination that the forwarding rate of the unoccupied queue exceedsthe forwarding rate of each of the other queues.
 7. The network deviceof claim 1, where the processor is further to: identify another declaredtransfer rate associated with another connection request, of theplurality of connection requests, containing other particular trafficparameters, determine, based on the other particular traffic parameters,other particular queues, of the set of queues, having forwarding ratesthat are not greater than the other declared transfer rate, determinethat the forwarding rate of a first particular queue, of the otherparticular queues, exceeds the forwarding rate of each the otherparticular queues, determine that the first particular queue isoccupied, and deny, based on the determination that the first particularqueue is occupied, the other connection request.
 8. A system comprising:a set of queues to buffer data associated with a plurality of connectionrequests, received at the network device, from a plurality of terminals;a memory to store a plurality of instructions; and one or more devicesto execute the plurality of instructions, where the plurality ofinstructions comprise: instructions to identify a declared transfer rateassociated with a particular connection request, of the plurality ofconnection requests, containing particular traffic parameters,instructions to determine, based on the particular traffic parameters,particular queues, of the set of queues, having forwarding rates thatare not greater than the declared transfer rate, and instructions toassign an unoccupied queue, of the particular queues, to the connectionrequest.
 9. The system of claim 8, where the system comprises a gatewayconnecting first terminals, of the plurality of terminals, associatedwith a local access network (LAN), to second terminals, of the pluralityof terminals, associated with a wide area network (WAN).
 10. The systemof claim 8, where the particular traffic parameters comprise at leastone of a variable bit rate (VBR) or an available bit rate (ABR).
 11. Anetwork device, comprising: an interface to receive a connection requestcomprising a plurality of data units, the connection request includingan indication of a transfer type; and a connection assignment sectionto: determine whether the transfer type is a first transfer type;identify, when the transfer type is the first transfer type, a declaredtransfer rate for a connection associated with the connection request;select a particular queue, of a plurality of queues associated with thefirst transfer type that each have a forwarding rate that does notexceed the declared transfer rate; and determine whether the firsttransfer type is a first sub-type, where, when the first transfer typeis the first sub-type, the connection assignment section is further to:determine whether the particular queue is occupied, and forward, whenthe particular queue is not occupied, at least some of the data units tothe particular queue.
 12. The network device of claim 11, where, whennone of the plurality of queues has a forwarding rate that does notexceed the declared transfer rate, the connection assignment section isto deny the connection request.
 13. The network device of claim 11,where, when the at least one queue is occupied, the connectionassignment section is to deny the connection request.
 14. The networkdevice of claim 11, where the connection assignment section is furtherto: determine whether the forwarding rate of another one of the queuesassociated with the first transfer type is not greater than the declaredtransfer rate; and grant the connection request when the forwarding rateof the other one queue is not greater than the declared transfer rate.15. The network device of claim 11, where, when the indication includespeak cell rate information, the first transfer type is the firstsub-type.
 16. The network device of claim 11, where the connectionassignment section is further to: determine whether the first transfertype is a second sub-type, and where, when the indication includes atleast one of variable bit rate information or available bit rateinformation the first transfer type is a second sub-type.
 17. Thenetwork device of claim 16, where, when the first transfer type is thesecond sub-type, the one or more devices are further to grant theconnection request when the at least one queue is occupied orunoccupied.
 18. The network device of claim 11, where, when the at leastone queue has a forwarding rate that is not greater than the declaredtransfer rate, the one or more devices are further to: select the atleast one queue for receiving at least some of the data units, theforwarding rate of the at least one queue being equal to or greater thanrespective forwarding rates of non-selected queues associated with thefirst transfer type.
 19. The network device of claim 11, where the oneor more devices are further to: determine whether the first transfertype is a pre-determined transfer type; select, when the transfer typeis the predetermined transfer type, a predetermined queue; and forwardat least some of the data units to the selected predetermined queue. 20.The network device of claim 11, where, the indication comprises virtualconnection information, the one or more devices are further to select anoutput line for transfer of at least some of the data units based on thevirtual connection information.